Exhaust gas which is discharged from an internal combustion engine, for example, a gasoline engine or a diesel engine for an automobile and the like, contains harmful components such as carbon monoxide (CO), hydrocarbon (HC) and nitrogen oxide (NOx).
Therefore, an exhaust gas purifying apparatus for decomposing and removing such harmful components is provided in the internal combustion engine, and most of the harmful components are substantially rendered harmless by an exhaust gas purifying catalyst installed in the exhaust gas purifying apparatus.
As such an exhaust gas purifying catalyst, for example, a NOx storage reduction catalyst is known, which is a catalyst in which NOx in exhaust gas is stored in a lean atmosphere and is reduced in a stoichiometric or rich atmosphere to nitrogen (N2), and utilizes a change of exhaust gas components among lean, stoichiometric and rich atmospheres.
However, NOx purification in a lean atmosphere is still a problem to be solved, and various studies have been made.
Prior Art Document 1 discloses a ceramic catalyzer where catalyst particles are loaded on ceramic supports and a layer containing Ta as an evapotranspiration-resistant metal is provided on at least part of the outer surface of the catalyst particle so as to prevent evapotranspiration of the catalyst particle.